Exam 3: Topic 9 Flashcards
when do humans have the most plasticity?
right after birth there is an explosion of dendrites and then pruning occurs
- The human brain has 100 billion neurons, 600 trillion synapses (adults), and 1,000 trillion (quadrillion) synapses in young children
what phenomena occur during development of the nervous system? (4)
- Formation of brain regions
- Neurogenesis
- Axonal growth
- Synaptogenesis
what are critical periods and modification to brain circuits based on?
experience
neural activity
sensory input and sensorimotor integration that allows adaptation and triggers the refinement of connections via calcium, neurotrophins, local gene expression, cytoskeleton, etc.
T/F Many basic physiological processes are innate or hardwired and require no experience
True
- like brainstem neural control of respiration
- For many behaviors there are specific points in the lifetime of the organism in which these behaviors can be learned
what do complex behaviors require?
neural activity for development
how do genetics influence brain circuits?
prenatal construction of neuron circuits and their highways are genetically specific and therefore controlled by genes
what are postnatal modifications of neuron circuits? (2)
- Adapt to changing external environments
- Temporal windows for the brain to become refractory to the lessons of experience ⇒ critical or sensitive periods
critical period
represents the limited times of postnatal development change elicited by electrical activity in specific circuits
- system, circuit, or cell waiting for specific instructional information from the environment
postnatal experience
patterns of neural activity
T/F If appropriate experience is not gained during the critical period, the pathway may still attain the ability to process certain forms of sensory information?
False it may never attain ability
- depth of an object, perception, etc. may be impaired permanently
T/F during a critical period the system can adapt to virtually any stimuli, appropriate or inappropriate?
True
how is it possible to delay/accelerate the critical period? (2)
- Environment via dark rearing
- Molecules via GABA
built in behaviors
experience is an on switch for these behaviors and will develop when prompted by the environment
- auditory, vision
- olfactory is more evolutionarily primitive
what are properties of critical periods? (9)
- Duration is proportional to lifespan
- Functional competition between inputs
- Neuronal activity ⇒ action potentials, forward and back propagating
- Structural consolidation of pathways
- Onset and duration is defined by neural activity
- Different critical periods for different systems
- Diversity of sensory/motor systems and molecular mechanisms
- Particular roles of excitation and inhibition ⇒ GABA can close the critical period
- Potential for reactivation ⇒ training, growth factors
congenital blindness
no neuron machinery to make light photons into electrical impulses and cannot gain vision
how does congenital blindness and braille reading affect neurons?
the back of the head has the visual cortex which lights up when looking at things and the primary visual cortex lights up when braille is done ⇒ not a use it or lose it situation
- The neocortex is very opportunistic and will use tissue for different purposes
how do blind vs not blind people have impacted memory performance?
superior verbal memory in congenitally blind subjects
- about 0.5% to 2% change in memory
who won the Nobel prize for discovering ocular dominance and brain plasticity?
Hubel and Weisel
- showed high plasticity immediately after birth and importance of rich stimuli to our brains
what is the path from the eye to the brain?
retina => optic tract ==> LGN => optic radiations => V1
- the primary visual cortex receives direct input from the visual thalamus
where does visual dependent plasticity occur?
in the V1 Cortex area not the retina or thalamus
are retinal neurons monocular or binocular? Thalamic? Cortical?
monocular; monocular; binocular
monocular
each of the two eyes are not interconnected
what layers are the binocular vs monocular cells in?
monocular are in layer 4 while binocular are in layer 2+3
ocular dominance columns
Axons from cells in the lateral geniculate nucleus serving each eye terminate in separate bands in layer 4 => these bands appear to alternate for left vs right eyes
how do you identify synaptic targets of information from the retina via ocular dominance columns?
inject radiolabeled amino acid proline into one eye and it will get incorporated into proteins and be transported across synapses
- See radioactive label (white) in specific areas of layer 4 in the visual cortex
- Dark areas are visual cortex that receives information from the unlabeled eye
T/F in typical adults, each eye has about equal territory of synapses in layer 4 relating to neurons for vision?
True
what happens to deprived eye columns after monocular deprivation?
eye columns are shrunken, not disappearing ⇒ competitive imbalance
- even with temporary eye closure there is still an effect
- light patches are non-deprived eye and these columns have expanded compared to the other side
T/F eyelid closure means that neural activity in that eyes retina goes to zero?
False
- There is still spontaneous neural activity in that deprived eye
how does monocular deprivation affect terminal arborizations?
in the LGN axons of the visual cortex, short term monocular deprivation and long term monocular deprivation both lead to less axon synapses on receiving cells
- the cells look much less dense and have fewer projections
T/F the ocular dominance assay rapid test where one eye is covered can cause monocular deprivation?
False its a rapid test that takes seconds to minutes not days
- It alone does not induce plasticity
what would neurons in layer 4 show up as on a histogram? Layer 2/3?
they would likely be more toward the edges of the histogram
- the layer 2/3 neurons are more in the middle as they will have a converged response from both eyes
how does monocular deprivation affect ocular dominance histograms?
it shifts the activated cells to either the ipsilateral or contralateral sides of the graph depending on where the electrode probe is placed in the brain
- Whether it shifts ipsilateral vs contralateral depends on which eye is patched and which eye is recorded ⇒ get contralateral if recorded from opposite hemisphere
when monocular deprivation occurs which eye do most of the cells respond to?
they respond to the eye that has not been covered
- we only see action potentials from the eye that is always open
- the synapses left over are not sufficient to drive past spike threshold and make the neurons fire
T/F Even 1 day of monocular deprivation can produce a shift in ocular dominance in a cat?
True
T/F there is a shift in the ocular dominance histogram if monocular deprivation occurs in adult mammals?
False only during the critical period
T/F there are competitive imbalance inputs with binocular deprivation?
False there are no competitive imbalances as they are both unstimulated
what drives ocular dominance plasticity?
competition and local correlations in neural activity
- even weak deprivation can produce a catastrophic shift
what pattern do we see regarding monocular deprivation and hebbian plasticity?
normally there are inputs to a neuron coming from both left and right cells, but when there is deprivation in one eye those inputs no longer come in
- the other inputs from the open eye will begin to cooperate and after a certain point the outcompeted inputs will not turn back on
what competition occurs in strabismus?
strabismic animals and humans will see with one eye at a time to prevent double vision and corrupted vision so inter-ocular conflict occurs from a lack of binocular convergence
- if two different stimuli are presented to each eye, the visual system gets confused and will shut down thalamic afferents from one eye
- Every 5-8 seconds your perception will switch from one eye to the other (binocular rivalry)
T/F the 2 + 3 cell layers will get strong inputs from both eyes during binocular rivalry?
False, none of the ⅔ layer cells will get strong inputs from both eyes at the same time
- Very few respond to stimulation of both eyes
- Not getting coincident input on the same cells
- if one eye deviates from the other eye fixating at a certain point, there is a constant conflict
what happens when you block NMDA receptors in the visual cortex during the critical period?
leads to a blocking of a shift in ocular dominance plasticity and changes dendrite structure without gene expression
- signaling to the nucleus is calcium dependent for gene expression and synaptic plasticity in general
- calcium will not enter the cell and thus synaptic cell activity will be halted
what ocular experiment confirmed hebbs postulate?
when a third eye was inserted into a frogs head on one side of the face, there was originally no competition between the two tectum regions in the brain, and then competition occurred on the opposite side of the brain where the transplanted eye and normal eye were located
- this led to an appearance of alternating columns for vision just like in higher mammals brains
how was ocular dominance plasticity tested in rats? Including the dark exposure?
rats underwent monocular deprivation during their critical period and then were taken swimming to find a hidden platform using visual cues
- dark exposure therapy for 10 days somewhat recovered the deprived eyes vision but impacted the rats visual acuity
- for rats who did not do dark exposure they had no recovery and could not find the hidden platform
- went from about 0.2 acuity to 0.6 acuity compared to 0.8 acuity for non deprived rats
closely spaced lines demonstrate what aspect of visual frequency?
high spatial frequency
widely spaced lines demonstrate what aspect of visual frequency?
low spatial frequency
T/F there is a competitive imbalance between two eyes for cortical territory with bilateral cataracts?
False there is no competitive imbalance for people who have bilateral cataracts
- Ocular dominance should be perfectly normal but other plasticity has been affected
what side effects do people with bilateral cataract removal during adulthood have?
contrast boarders in objects are treated as independent instead of as a whole object
- such as spots on a cow each being their own object
- they have object and “figure from ground” blindness
what does exposing a young mouse to a single tone frequency result in?
the expansion of the territory in which auditory cortical neurons are responsive to that tone, at the expense of the representation of other tones with lower or higher frequencies
- When having prolonged exposure to a certain frequency during the critical period there will be more neurons in that particular frequency auditory cortex
what is the difference in hand babbling for deaf infants vs normal hearing infants?
deaf infants raised by deaf parents using ASL compared to hearing babies will use more babbling with their hands and fingers to replace vocal babbling in hearing infants
how does age affect learning a language when immigrating somewhere new?
immigrants learning english have an easy time prior to the age of 3 but afterward there is a steady decline in ability to learn and speak like a native speaker
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